Action Constraint: add Split Channels Mix choices from Copy Transforms

Practice shows that when combining actions and direct animation
it is usually best to combine location, rotation and scale
separately, which is implemented by the Split Channels modes
recently introduced in D9469 for Copy Transforms. This completes
the same set of 6 choices for the Action Constraint.

The default for new constraints is changed to the newly
added Before Original (Split Channels) mode.

The original patch is motivated by Loic Pinsard, who created
an addon that does the equivalent of this feature by splitting
the action into two, separating location and rotation+scale.

Differential Revision: https://developer.blender.org/D7547

4 files changed, 73 insertions, 16 deletions

diff --git a/source/blender/blenkernel/intern/constraint.c b/source/blender/blenkernel/intern/constraint.c
index b7e02f06571..0da29ded13d 100644
--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -2982,6 +2982,16 @@ static void actcon_evaluate(bConstraint *con, bConstraintOb *cob, ListBase *targ
 
   if (VALID_CONS_TARGET(ct) || data->flag & ACTCON_USE_EVAL_TIME) {
     switch (data->mix_mode) {
+      /* Simple matrix multiplication. */
+      case ACTCON_MIX_BEFORE_FULL:
+        mul_m4_m4m4(cob->matrix, ct->matrix, cob->matrix);
+        break;
+
+      case ACTCON_MIX_AFTER_FULL:
+        mul_m4_m4m4(cob->matrix, cob->matrix, ct->matrix);
+        break;
+
+      /* Aligned Inherit Scale emulation. */
       case ACTCON_MIX_BEFORE:
         mul_m4_m4m4_aligned_scale(cob->matrix, ct->matrix, cob->matrix);
         break;
@@ -2990,8 +3000,13 @@ static void actcon_evaluate(bConstraint *con, bConstraintOb *cob, ListBase *targ
         mul_m4_m4m4_aligned_scale(cob->matrix, cob->matrix, ct->matrix);
         break;
 
-      case ACTCON_MIX_AFTER_FULL:
-        mul_m4_m4m4(cob->matrix, cob->matrix, ct->matrix);
+      /* Fully separate handling of channels. */
+      case ACTCON_MIX_BEFORE_SPLIT:
+        mul_m4_m4m4_split_channels(cob->matrix, ct->matrix, cob->matrix);
+        break;
+
+      case ACTCON_MIX_AFTER_SPLIT:
+        mul_m4_m4m4_split_channels(cob->matrix, cob->matrix, ct->matrix);
         break;
 
       default:
@@ -5767,6 +5782,17 @@ static bConstraint *add_new_constraint(Object *ob,
       }
       break;
     }
+    case CONSTRAINT_TYPE_ACTION: {
+      /* The Before or Split modes require computing in local space, but
+       * for objects the Local space doesn't make sense (T78462, D6095 etc).
+       * So only default to Before (Split) if the constraint is on a bone. */
+      if (pchan) {
+        bActionConstraint *data = con->data;
+        data->mix_mode = ACTCON_MIX_BEFORE_SPLIT;
+        con->ownspace = CONSTRAINT_SPACE_LOCAL;
+      }
+      break;
+    }
   }
 
   return con;
diff --git a/source/blender/editors/transform/transform_convert.c b/source/blender/editors/transform/transform_convert.c
index 00fd008151d..e77fedfe143 100644
--- a/source/blender/editors/transform/transform_convert.c
+++ b/source/blender/editors/transform/transform_convert.c
@@ -861,10 +861,13 @@ bool constraints_list_needinv(TransInfo *t, ListBase *list)
           /* The Action constraint only does this in the Before mode. */
           bActionConstraint *data = (bActionConstraint *)con->data;
 
-          if (ELEM(data->mix_mode, ACTCON_MIX_BEFORE) &&
+          if (ELEM(data->mix_mode, ACTCON_MIX_BEFORE, ACTCON_MIX_BEFORE_FULL) &&
               ELEM(t->mode, TFM_ROTATION, TFM_TRANSLATION)) {
             return true;
           }
+          if (ELEM(data->mix_mode, ACTCON_MIX_BEFORE_SPLIT) && ELEM(t->mode, TFM_ROTATION)) {
+            return true;
+          }
         }
         else if (con->type == CONSTRAINT_TYPE_TRANSFORM) {
           /* Transform constraint needs it for rotation at least (r.57309),
diff --git a/source/blender/makesdna/DNA_constraint_types.h b/source/blender/makesdna/DNA_constraint_types.h
index a77fbc9e45e..822b8705c9b 100644
--- a/source/blender/makesdna/DNA_constraint_types.h
+++ b/source/blender/makesdna/DNA_constraint_types.h
@@ -901,10 +901,16 @@ typedef enum eActionConstraint_Flags {
 typedef enum eActionConstraint_MixMode {
   /* Multiply the action transformation on the right. */
   ACTCON_MIX_AFTER_FULL = 0,
+  /* Multiply the action transformation on the left. */
+  ACTCON_MIX_BEFORE_FULL = 3,
   /* Multiply the action transformation on the right, with anti-shear scale handling. */
   ACTCON_MIX_AFTER = 1,
   /* Multiply the action transformation on the left, with anti-shear scale handling. */
   ACTCON_MIX_BEFORE = 2,
+  /* Separately combine Translation, Rotation and Scale, with rotation on the right. */
+  ACTCON_MIX_AFTER_SPLIT = 4,
+  /* Separately combine Translation, Rotation and Scale, with rotation on the left. */
+  ACTCON_MIX_BEFORE_SPLIT = 5,
 } eActionConstraint_MixMode;
 
 /* Locked-Axis Values (Locked Track) */
diff --git a/source/blender/makesrna/intern/rna_constraint.c b/source/blender/makesrna/intern/rna_constraint.c
index a0a0a41b58d..e36d052d27c 100644
--- a/source/blender/makesrna/intern/rna_constraint.c
+++ b/source/blender/makesrna/intern/rna_constraint.c
@@ -679,7 +679,7 @@ static void rna_ActionConstraint_mix_mode_set(PointerRNA *ptr, int value)
   acon->mix_mode = value;
 
   /* The After mode can be computed in world space for efficiency
-   * and backward compatibility, while Before requires Local. */
+   * and backward compatibility, while Before or Split requires Local. */
   if (ELEM(value, ACTCON_MIX_AFTER, ACTCON_MIX_AFTER_FULL)) {
     con->ownspace = CONSTRAINT_SPACE_WORLD;
   }
@@ -1773,25 +1773,47 @@ static void rna_def_constraint_action(BlenderRNA *brna)
   };
 
   static const EnumPropertyItem mix_mode_items[] = {
+      {ACTCON_MIX_BEFORE_FULL,
+       "BEFORE_FULL",
+       0,
+       "Before Original (Full)",
+       "Apply the action channels before the original transformation, as if applied to an "
+       "imaginary parent in Full Inherit Scale mode. Will create shear when combining rotation "
+       "and non-uniform scale"},
       {ACTCON_MIX_BEFORE,
        "BEFORE",
        0,
-       "Before Original",
-       "Apply the action channels before the original transformation, "
-       "as if applied to an imaginary parent with Aligned Inherit Scale"},
-      {ACTCON_MIX_AFTER,
-       "AFTER",
+       "Before Original (Aligned)",
+       "Apply the action channels before the original transformation, as if applied to an "
+       "imaginary parent in Aligned Inherit Scale mode. This effectively uses Full for location "
+       "and Split Channels for rotation and scale"},
+      {ACTCON_MIX_BEFORE_SPLIT,
+       "BEFORE_SPLIT",
        0,
-       "After Original",
-       "Apply the action channels after the original transformation, "
-       "as if applied to an imaginary child with Aligned Inherit Scale"},
+       "Before Original (Split Channels)",
+       "Apply the action channels before the original transformation, handling location, rotation "
+       "and scale separately"},
+      {0, "", 0, NULL, NULL},
       {ACTCON_MIX_AFTER_FULL,
        "AFTER_FULL",
        0,
-       "After Original (Full Scale)",
-       "Apply the action channels after the original transformation, as if "
-       "applied to an imaginary child with Full Inherit Scale. This mode "
-       "can create shear and is provided only for backward compatibility"},
+       "After Original (Full)",
+       "Apply the action channels after the original transformation, as if applied to an "
+       "imaginary child in Full Inherit Scale mode. Will create shear when combining rotation "
+       "and non-uniform scale"},
+      {ACTCON_MIX_AFTER,
+       "AFTER",
+       0,
+       "After Original (Aligned)",
+       "Apply the action channels after the original transformation, as if applied to an "
+       "imaginary child in Aligned Inherit Scale mode. This effectively uses Full for location "
+       "and Split Channels for rotation and scale"},
+      {ACTCON_MIX_AFTER_SPLIT,
+       "AFTER_SPLIT",
+       0,
+       "After Original (Split Channels)",
+       "Apply the action channels after the original transformation, handling location, rotation "
+       "and scale separately"},
       {0, NULL, 0, NULL, NULL},
   };